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It is highly desirable to design efficient and stable hydrogen evolution reaction (HER) and oxygen evolution/reduction reaction (OER/ORR) electrocatalysts for the development of renewable energy technologies. Herein, density functional theory (DFT) calculations were conducted to systematically investigate a series of TMNxO4−x-HTT (TM = Fe, Co, Ni, Ru, Rh, Pd, Ir and Pt; HTT = hexahydroxy tetraazanaphthotetraphene) analogs of two-dimensional (2D) conductive metal-organic frameworks (MOFs) as potential electrocatalysts for the HER, OER and ORR. The thermodynamic and electrochemical stability simulations suggest that these designed catalysts are stable. Remarkably, CoO4-HTT, RhN3O1-HTT and IrN3O1-HTT are predicted to be the most promising catalysts for the HER, OER and ORR, respectively, surpassing the catalytic activity of corresponding benchmark catalysts. The volcano plots were established based on the scaling relationship of adsorption Gibbs free energy of intermediates. The results reveal that regulating combinations of metal active centers and local coordination environments could effectively balance the interaction strength between intermediates and catalysts, thus achieving optimal catalytic activity. Our findings not only opt for the promising HER/OER/ORR electrocatalysts but also guide the design of efficient electrocatalysts based on 2D MOFs materials. [ABSTRACT FROM AUTHOR]

Precise design and synthesis of sub-nano scale catalysts with controllable electronic and geometric structures are pivotal for enhancing the hydrogen evolution reaction (HER) performance of molybdenum sulfide (MoS2) and unraveling its structure-activity relationship. By leveraging transition molybdenum polysulfide clusters as functional units for multi-level ordering, we successfully designed and synthesized MoSx nanowire networks derived from [Mo3S13]2− clusters via evaporation-induced self-assembly, which exhibit enhanced HER activity attributed to a high density of active sites and dynamic evolution behavior under cathodic potentials. MoSx nanowire networks electrode yields a current density of 100 mA·cm−2 at 142 mV in 0.5 M H2SO4. This work provides an attractive prospect for optimizing catalysts at the sub-nano scale and offers insights into a strategy for designing catalysts in various gas evolution reactions. [ABSTRACT FROM AUTHOR]

The exfoliation of bulk 2H-molybdenum disulfide (2H-MoS2) into few-layer nanosheets with 1T-phase and controlled layers represents a daunting challenge towards the device applications of MoS2. Conventional ion intercalation assisted exfoliation needs the use of hazardous n-butyllithium and/or elaborate control of the intercalation potential to avoid the decomposition of the MoS2. This work reports a facile strategy by intercalating Li ions electrochemically with ether-based electrolyte into the van der Waals (vdW) channels of MoS2, which successfully avoids the decomposition of MoS2 at low potentials. The co-intercalation of Li+ and the ether solvent into MoS2 makes a first-order phase transformation, forming a superlattice phase, which preserves the layered structure and hence enables the exfoliation of bulk 2H-MoS2 into bilayer nanosheets with 1T-phase. Compared with the pristine 2H-MoS2, the bilayer 1T-MoS2 nanosheets exhibit better electrocatalytic performance for the hydrogen evolution reaction (HER). This facile method should be easily extended to the exfoliation of various transition metal dichalcogenides (TMDs). [ABSTRACT FROM AUTHOR]

Doping foreign metal atoms into the substrate of transition metal dichalcogenides (TMDs) enables the formation of diverse atomic structure configurations, including isolated atoms, chains, and clusters. Therefore, it is very important to reasonably control the atomic structure and determine the structure–activity relationship between the atomic configurations and the hydrogen evolution reaction (HER) performance. Although numerous studies have indicated that doping can yield diverse atomic structure configurations, there remains an incomplete understanding of the relationship between atomic configurations within the lattice of TMDs and their performance. Here, diverse atomic structure configurations of adsorptive doping, substitutional doping, and TMDs alloys are summarized. The structure–activity relationship between different atomic configurations and HER performance can be determined by micro-nanostructure devices and density functional theory (DFT) calculations. These diverse atomic structure configurations are of great significance for activating the inert basal plane of TMDs and improving the catalytic activity of HER. Finally, we have summarized the current challenges and future opportunities, offering new perspectives for the design of highly active and stable metal-doped TMDs catalysts. [ABSTRACT FROM AUTHOR]

Vertically stacking two-dimensional (2D) materials with small azimuthal deviation or lattice mismatch generate distinctive global structural periodicity and symmetry, revealed as the moiré superlattices (MSLs). Manipulating the interlayer twist angle enables the modification of the electronic structure of 2D materials to explore the advanced applications. Although extraordinary progress has been achieved in the unique structure and emergent properties of MSLs, the investigation of the catalytic applications of MSLs materials is still in its infancy. It is therefore very urgent to summarize the advanced development of MSLs in the field of catalysis. In this review, we firstly summarize the advanced fabrication and high-resolution characterization techniques of the MSLs materials, as well as their novel properties related to catalysis represented by electrocatalytic hydrogen evolution reaction (HER). Then, all the MSLs materials such as MoS2, WS2, and Ru serving as electrocatalysts for HER are further reviewed in detail. Finally, we outline the current challenges as well as the experimental and theoretical strategies to advance the development of function-oriented MSLs materials for catalysis. This review aims to provide profound insight into the wide applications of this novel material platform in catalytic field. [ABSTRACT FROM AUTHOR]

Semiconductors-based heterogeneous photocatalytic water splitting has been extensively studied, but it still remains challenging to accelerate the separation of electron—hole pairs and facilitate the reaction kinetics. Here we report a general strategy to fabricate highly efficient Pt/TiO2 photocatalyst by coupling the Pt co-catalysts and surface oxygen vacancies (VO) of TiO2. TiO2 was pre-modified with alkali or alkaline earth metals ion solutions, which produce a large number of surface hydroxyl on TiO2. Subsequently, the photodeposited Pt sub-nanoparticles substitute surface hydroxyl and induce surface VO on TiO2. The coupling of Pt and surface VO on TiO2 can accelerate the extraction of photo-charges through the interaction of Pt—VO—Ti bonds and reduce the hydrogen evolution barrier, thereby promoting the photocatalytic activity. The synthesized Pt-VO-TiO2 sample exhibits a photocatalytic hydrogen evolution activity as high as 1.5 L·g−1·h−1, which is 2.2 times that of traditional Pt/TiO2. Our findings in-depth understand the synergistic effect of co-catalysts and defects on photocatalysis and open up new possibilities for achieving robust photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

The sufficient utilization of Mott-Schottky effect for boosting alkaline hydrogen evolution reaction (HER) depends upon scale minimizing of interface components and exposure maximizing of Mott-Schottky interface. Here, a self-standing porous tubular Mott-Schottky electrocatalyst is constructed by a self-template etching strategy, where amorphous WOx (a-WOx) nano-matrix connects Co nanoparticles. This novel "Janus" electrocatalyst maximizes the Mott-Schottky effect by not only providing a highly exposed micro interface, but also simultaneously accelerating the water dissociation and optimizing the hydrogen desorption process. Experimental findings and theoretical calculations reveal that Co/a-WOx Mott-Schottky heterointerface triggers the electron redistribution and a build-in electric field, which can not only optimize the adsorption energy of the reaction intermediates, but also facilitate the charge transfer. Thus, Co/a-WOx requires an overpotential of only 36.3 mV at 10 mA·cm−2 and shows a small Tafel slope of 53.9 mV·dec−1 as well as an excellent 200-h long-term stability. This work provides a novel design strategy for maximizing the Mott-Schottky effect on promoting alkaline HER. [ABSTRACT FROM AUTHOR]

It is important to develop economical and durable electrocatalysts for sustainable energy conversion technology. However, the current catalysts still suffer from insufficient hydrogen adsorption energy. Herein, we report a kind of novel bi-phosphide catalyst through constructing heterogeneous structures and cation doping. The obtained sample delivers an outstanding hydrogen evolution reaction (HER) performance at all pH range. As oxygen evolution reaction (OER) electrocatalyst, Fe-CoP@Ni2P samples show an overpotential of 237 mV at 50 mA·cm−2 in alkaline solution. For electrolysis of water, Fe-CoP@Ni2P catalysts deliver a cell voltage of 1.59 V at 50 mA·cm−2 and long durability. Furthermore, density functional theory (DFT) calculation further confirms that the doped heterostructure promotes Gibbs free energy for hydrogen adsorption. And the significant increase in the density of total states (DOS) also enhances the catalytic activity of HER. [ABSTRACT FROM AUTHOR]

With practical electrocatalytic hydrogen production frequently involving the splitting of water in various pH media, there is an urgent need but still a technical challenge to develop low-cost, highly active, and stable electrocatalysts for pH-universal hydrogen evolution reaction (HER). We report herein the adoption of a hydrothermal reaction combined with a post gas-phase doping strategy to fabricate P-doped NiCo2Se4 hollow nanoneedle arrays on carbon fiber paper (i.e., P−NiCo2Se4/CFP). Notably, the optimal arrays (P8.71−NiCo2Se4/CFP) can afford an outstanding pH-universal HER performance, with an overpotential as low as 33, 57, and 69 mV at 10 mA·cm−2 and corresponding Tafel slopes down to 52, 61, and 72 mV·dec−1 in acidic, alkaline, and neutral media, respectively, outperforming most state-of-the-art nonprecious catalysts and even the commercial Pt/C catalyst in both neutral and alkaline media at large current densities. Impressively, P8.71−NiCo2Se4/CFP also displays good durability toward long-time stability testing in harsh acidic and alkaline electrolytes. Experimental and theoretical studies further reveal that the doping of P atoms into NiCo2Se4 can simultaneously optimize its H* adsorption/desorption energy, water adsorption energy, and water dissociation energy by adjusting the local electronic states of various active sites, thus accelerating the rate-determining step of HER in different pH media to endow P−NiCo2Se4 with an outstanding pH-universal HER performance. This work provides atomic-level insights into the roles of active sites in various electrolysis environments, thereby shedding new light on the rational design of highly efficient pH-universal nonprecious catalysts for HER and beyond. [ABSTRACT FROM AUTHOR]

Creating vacancy is often highly effective in enhancing the hydrogen evolution performance of transition metal-based catalysts. Vacancy-rich Ni nanosheets have been fabricated via topochemical formation of two-dimentional (2D) Ni2B on graphene precursor followed by boron leaching. Anchored on graphene, a few atomic layered Ni2B nanosheets are first obtained by reduction and annealing. Large number of atomic vacancies are then generated in the Ni2B layer via leaching boron atoms. When used for hydrogen evolution reaction (HER), the vacancy-rich Ni/Ni(OH)2 heterostructure nanosheets demonstrate remarkable performance with a low overpotential of 159 mV at a current density of 10 mA·cm−2 in alkaline solution, a dramatic improvement over 262 mV of its precursor. This enhancement is associated with the formation of vacancies which introduce more active sites for HER along Ni/Ni(OH)2 heterointerfaces. This work offers a facile and universal route to introduce vacancies and improve catalytic activity. [ABSTRACT FROM AUTHOR]

Molybdenum phosphide is a potential hydrogen evolution reaction (HER) catalyst. However, traditional high-temperature phosphating preparation methods are prone to damage of material morphology and agglomeration. Using the carbon skeleton to limit the size and morphology of MoP and to improve the conductivity of the material is an effective method to improve the performance of the catalyst. However, there is a lack of research on the effect of carbon skeleton and MoP composite structure on the catalytic mechanism of HER. We coated ZIF-8 on the surface of MoP nanorods, and obtained open N-doped carbon-coated porous MoP nanorods (N/C/MoP) through carbonization and phosphating. Studies have shown that the ZIF-8 coating effectively limits the size and morphology of the material and avoids agglomeration. Under alkaline conditions, N/C/MoP has a low overpotential of 169 mV for HER at 10 mA/cm2, which is 55 mV lower than MoP without a carbon layer. At the same time, its Tafel slope (51.3 mV/dec) is smaller than Pt/C (59.9 mV/dec), and it has good stability. Density functional theory (DFT) studies have shown that under alkaline conditions, there is a synergistic effect between the open N-doped carbon layer and the exposed MoP active surface, which reduces the activation energy of water and improves the catalytic performance of HER. It is worth noting that a tight coating will hinder the exposure of active sites and reduce catalytic activity. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) has been recognized as one of the most promising candidates to replace precious Pt for hydrogen evolution reaction (HER) catalysis, due to the natural abundance, low cost, tunable electronic properties, and excellent chemical stability. Although notable processes have been achieved in the past decades, their performance is still far less than that of Pt. Searching effective strategies to boosting their HER performance is still the primary goal. In this review, the recent process of the electronic regulation of MoS2 for HER is summarized, including band structure engineering, electronic state modulation, orbital orientation regulation, interface engineering. Last, the key challenges and opportunities in the development of MoS2-based materials for electrochemical HER are also discussed. [ABSTRACT FROM AUTHOR]

Hetero-nanostructures of plasmonic metals and semiconductors have attracted increasing attention in the field of photocatalysis. However, most of the hetero-nanostructured catalysts are randomly arranged and therefore require comprehensive structural design for optimizing their properties. Herein, we report the robust construction of hierarchical hetero-nanostructures where gold (Au) nanorods and molybdenum disulfide (MoS2) quantum sheets (QSs) are integrated in highly ordered arrays. Such construction is achieved through porous anodic alumina (PAA) template-assisted electrodeposition. The as-fabricated hetero-nanostructures demonstrate exciting electrocatalysis towards hydrogen evolution reaction (HER). Both plasmon-induced hot-electron injection and plasmonic scattering/reabsorption mechanisms are determinative to the enhanced electrocatalytic performances. Notably, broadband photoresponses of HER activity in the visible range are observed, indicating their superiority compared with random systems. Such integrated hetero-nanoelectrodes could provide a powerful platform for conversion and utilization of solar energy, meanwhile would greatly prompt the production and exploration of ordered nanoelectrodes. [ABSTRACT FROM AUTHOR]

Developing non-precious metal catalysts with high activity and stability for electrochemical hydrogen evolution reaction (HER) is of great significance in both science and technology. In this work, N-doped CMK-3, which was prepared with a casting method using SBA-15 as the hard template and ammonia as the nitrogen source, has been utilized to hold MoS2 and restrict its growth to form MoS2@N-CMK-3 composite. As a result, MoS2 was found to have poorly crystallized and the limited space of porous N-CMK-3 made its size much small. Then there are more active sites in MoS2. Accordingly, MoS2@N-CMK-3 has exhibited good electrocatalytic performance toward HER in acids with a quite small Tafel slope of 32 mVdec"1. And more importantly, compared to MoS2@CMK-3, its stability has been greatly improved, which can be attributed to the interaction between MoS2 and nitrogen atoms avoiding aggregation and mass loss. This work provides an idea that doping a porous carbon support with nitrogen is an effective way to enhance the stability of the catalyst. [ABSTRACT FROM AUTHOR]

Controlled synthesis of structurally anisotropic rhenium diselenide (ReSe2) with macroscopically uniform and strictly monolayer thickness as well as tunable domain shape/size is of great interest for electronics-, optoelectronics-, and electrocatalysis-related applications. Herein, we describe the controlled synthesis of uniform monolayer ReSe2 flakes with variable morphology (sunflower- or truncated-triangle-shaped) on SiO2/Si substrates using different ambient-pressure chemical vapor deposition (CVD) setups. The prepared polycrystalline ReSe2 flakes were transferred intact onto Au foil electrodes and tested for activity in the hydrogen evolution reaction (HER). Interestingly, compared to the compact truncated-triangle-shaped ReSe2 flakes, their edge-abundant sunflower-shaped counterparts exhibited superior electrocatalytic HER activity, featuring a relatively low Tafel slope of ∼76 mV/dec and an exchange current density of 10.5 μA/cm2. Thus, our work demonstrates that CVD-grown ReSe2 is a promising two-dimensional anisotropic material for applications in the electrocatalytic HER. [ABSTRACT FROM AUTHOR]

The development of new non-precious metal catalysts and understanding the origin of their activity for the hydrogen evolution reaction (HER) are essential for rationally designing highly active low-cost catalysts as alternatives to state-of-the-art precious metal catalysts. Herein, manganese oxide/hydroxide was demonstrated as a highly active electrocatalysts for the HER by fabricating MnO2 nanosheets coated with Cu2O nanowire arrays (Cu2O@MnO2 NW@NS) on Cu foam followed by an in situ chronopotentiometry (CP) treatment. It was discovered that the in situ transformation of Cu2O@MnO2 into Cu@Mn(OH)2 NW@NS by the CP treatment drastically boosted the catalytic activity for the HER due to an enhancement of its intrinsic activity. Together with the benefits from such three-dimensional (3D) core-shell arrays for exposing more accessible active sites and efficient mass and electron transfers, the resulting Cu@Mn(OH)2 NW@NS exhibited excellent HER activity and outstanding durability in terms of a low overpotential of 132 mV vs. RHE at 10 mA/cm2. Overall, we expect these findings to generate new opportunities for the exploration of other Mn-based nanomaterials as efficient electrocatalysts and enable further understanding of their catalytic processes. [ABSTRACT FROM AUTHOR]

Integration of molybdenum disulfide (MoS) onto high surface area photocathodes is highly desired to minimize the overpotential for the solar-powered hydrogen evolution reaction (HER). Semiconductor nanowires (NWs) are beneficial for use in photoelectrochemistry because of their large electrochemically available surface area and inherent ability to decouple light absorption and the transport of minority carriers. Here, silicon (Si) NW arrays were employed as a model photocathode system for MoS wrapping, and their solar-driven HER activity was evaluated. The photocathode is made up of a well-defined MoS/TiO/Si coaxial NW heterostructure, which yielded photocurrent density up to 15 mA/cm (at 0 V vs. the reversible hydrogen electrode (RHE)) with good stability under the operating conditions employed. This work reveals that earth-abundant electrocatalysts coupled with high surface area NW electrodes can provide performance comparable to noble metal catalysts for photocathodic hydrogen evolution. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]